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IGTI is pleased to announce the theme of the Turbo Expo 2009
keynoteaddress, Gas Turbine Technologies: Meeting Complex Global
Challenges.Executive Conference Chair Barry Nicholls, Vice
President of Siemens Power
Systems Sales, Siemens Power Generation, Inc., helped direct the
focus of thekeynote. IGTI asked Nicholls to elaborate on the
theme:
Q: Why do you think the keynote topic “Gas Turbine Technologies:
MeetingComplex Global Challenges” is so relevant/important to the
gas turbine industryright now?
A: Today we live in a constant and rapidly changing global
environment rootedin the surging information age. As a result, to
keep customers satisfied, develop-ment and implementation horizons
are decreasing at the same time the level ofperformance (power and
efficiency) must continuously increase. What wecurrently face with
gas turbines is an analogous situation to Moore’s law
fortransistors and other computer hardware, perhaps a bit less
aggressive though!The only way to meet this challenge is with
aggressive technology innovationand implementation lead by
excellent employees and fundamentally strongcustomer interaction.
When you add to this environment a significant (and
fill the global power gapin the coming years.Another possible
concernis political uncertainty inthe area of carbon legis-lation
and emission con-trols, a lot hangs in thebalance right now as
tohow this legislation is approached and executed andthe effect on
the global energy portfolio balancebetween gas turbines, coal,
nuclear and renewables.A third concern is staffing; it is becoming
more andmore difficult to find and retain qualified engineers.Some
concerns I’ve heard lately coming from theengineering community is
“who’s going to do allthis work?” It’s something we still don’t
have a long-term answer for, since the trend of university
grad-uates is currently not in favor of engineering.
Q: What are some energy-efficient, “clean” tech-nologies
currently in development in the gas turbineindustry?
A: A lot of emphasis is being placed on highhydrogen fuels
(pre-combustion carbon seques-tration of gasified coal [IGCC]), and
carbon neutralbio fuels in low emission applications by
thedepartment of energy. We see these as areas ofgrowth in the
future and the right thing to do, so weare actively participating
with the DOE in theseprograms and on our own. We also see
technologybreakthroughs coming in the areas of combustionand
turbine engineering, materials and post com-bustion gas treatment
that will be cost effectivegame changers for emissions, power and
efficiency.
Q: What role does Turbo Expo play in shapingR&D solutions
for industry challenges? Is thereanything that Turbo Expo should do
to expand itsrole in 2009 and beyond?
A: Turbo Expo is a great forum to get the majorplayers in the
gas turbine world together and havetechnical discussions and
collaborations. It allowsengineers from the power generation side
to attendtalks by aero engineers and vice versa; this is a goodway
to stimulate bottom line innovation. As anOEM, we would always like
to see increased end userattendance at the Turbo Expo event. ✲
December 2008 Global Gas Turbine News 1
ATLANTA, GEORGIA USA • ASME INTERNATIONAL GAS TURBINE
INSTITUTE
Volume 48, No. 4 • December 2008
I N TH ISISSU E.. .Calendar of Events
2Aircraft Engine
Thermal Management:The Impact of Aviation
Electric Power Demands
2-3Compact Gas TurbineCombustion Research
4-5Opportunity Fuelsand Combustion
5-6Professional Development
7
SPECIAL SUPPLEMENT
EXECUTIVE CONFERENCECHAIR
BARRY NICHOLLS
Turbo Expo 2009 KeynoteTheme Announced
growing) variation and cost in global fuel sources,power plant
flexibility requirements and regionallystringent emission
legislation, you run into asituation where it is “mission critical”
to not onlyhave technology innovation but also to create a suiteof
interchangeable proven technologies for a plat-form gas turbine
operation approach. As an example,we consistently find ourselves at
the edge oftemperatures, oxidation and corrosion limits ofturbine
materials, and the challenge is how todevelop and implement step
changes in thesesystems and integrate their design into the
turbinewith low risk across a worldwide fleet of engines.
Q: Aside from energy supply & cost, what areadditional
challenges facing gas turbine engineers inthe future?
A: Certainly you might say economic volatility andthe
possibility for a global slowdown have manyengineers questioning
future uncertainties, but I’mquite certain that’s true with most of
us at themoment. The next topic of discussion wouldprobably be:
what’s the future of gas turbines in aworld that talks so much
about renewable power?There is a very simple answer to that; power
demandcontinues to grow and while renewables are a greatsource of
energy going forward, they simply will notsignificantly lessen the
demand for clean gas turbinetechnology which we see as the
preferred option to
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2 Global Gas Turbine News December 2008
JANUARY 19-23, 2009Ultra Low NOx Gas TurbineCombustion
CourseWeetwood Hall ConferenceCentre & HotelOtley Road, Leeds,
UK
Organized by the University of Leeds,this course is designed for
combustiondesigners in gas turbine manufacturers;operators of
modern, low NOx electricalgeneration systems, including
combinedcycles; automotive emissions engineersand environmental
legislators andregulators. For more information
visitwww.engineering.leeds.ac.uk/cpd oremail:
[email protected].
MARCH 5-6, 2009The Gas Turbine: Principles andApplications Short
Course Amsterdam Marriott HotelAmsterdam, Netherlands
Calling design and developmentengineers, maintenance and
reliabilityengineers, project managers, Q&Apersonnel and
mechanical engineersworking with gas turbines! This two-daycourse
is about efficient evaluation of gasturbine performance for the
selectionand application of the right engine forthe job. Visit
http://www.asme.org/Education/Europe/Courses/Gas_Turbine_Principles
for more details.
June 6, 2009Basic Gas Turbine Metallurgy &Repair Technology
WorkshopWorld Center Marriott ResortOrlando, FL USA
Held in conjunction with Turbo Expoand instructed by Lloyd Cooke
and DougNagy, Liburdi Turbine Services.
June 6-7, 2009Physics-Based Internal Air SystemModeling Short
CourseWorld Center Marriott ResortOrlando, FL USA
Held in conjunction with Turbo Expoand instructed by Dr. Bijay
K. Sultanian,Siemens Energy, Inc.
June 6-7, 2009Gas Turbine Aerothermodynamics &Performance
Modeling Short CourseWorld Center Marriott ResortOrlando, FL
USA
Held in conjunction with Turbo Expoand instructed by Syed
Khalid, Rolls-Royce North America, this interactivecourse includes
tutorial sessions.
June 7, 2009Film Cooling & Technology for Gas Turbines
WorkshopWorld Center Marriott ResortOrlando, FL USA
Held in conjunction with Turbo Expoand conducted by VKI (Von
KarmanInstitute) and IGTI.
JUNE 8-12, 2009ASME Turbo Expo 2009Orlando World Marriott
Resortand Convention CenterOrlando, Florida USA
IGTI’s flagship event comprises a majorgas turbine conference
and exhibition.This 2009 event will be held at an all-inclusive
resort with golf course.
AUGUST 2-5, 200945th AIAA/ASME/SAE/ASEE JointPropulsion
Conference & Exhibit 7th Annual International EnergyConversion
Engineering Conference(IECEC)Colorado Convention CenterDenver,
CO
The objective for the Joint PropulsionConference is to identify
and highlightthe propulsion systems, components,and technologies
required to enable thenext generation of aerospace vehicles.The
IECEC conference provides a forumto present and discuss
engineeringaspects of energy conversion technology,advanced energy
and power systems,devices for terrestrial energy systems
andaerospace applications, and the policy,programs, and
environmental impactassociated with the development andutilization
of this technology.
FEBRUARY 201013th International Symposium onTransport Phenomena
and Dynamicsof Rotating Machinery (ISROMAC-13)Hawaii – more details
TBA
This conference deals with all aspects oftransport phenomena and
dynamics inrotating machinery, including research,design,
manufacturing, and operation. Itprovides a forum for presentation
of newand innovative technologies as well asfree exchange of ideas
among the worldleaders in rotating machinery.
JUNE 14-18, 2010ASME Turbo Expo 2010Scottish Exhibition &
Convention CentreGlasgow, Scotland
IGTI’s flagship event comprises a majorgas turbine conference
and exhibition.
AUGUST 7-13, 201014th Int’l Heat Transfer Conference(IHTC)Omni
Shoreham HotelWashington D.C., USA
CALENDAROF EVENTS
Traditionally, thermal management of aviation gasturbine engines
has been concentrated in the coreof the engine. Actively or
passively cooled regions inaircraft engine gas turbines include the
high-pressureturbine stationary vanes and rotating blades,
theshrouds bounding the rotating blades, the combustorliners and
flame holding segments, and the exhaustnozzle / after burner
system. Collectively thesecomponents are referred to as the hot gas
path. Suchengines additionally cool the interfaces around
theimmediate hot gas path using the secondary airflowcircuits of
the turbine wheel spaces and outer casings.The secondary fluid flow
systems also extend wellbeyond the core region including
thermalmanagement of the lube oil and bearings, deicingwithin the
compressor, and active clearance controlmeasures. Conventional
cooling technology, asapplied to gas turbine engine components,
iscomposed of internal convective cooling, externalsurface film
cooling, materials and coatings selection,
Aircraft Engine Thermal Management:The Impact of Aviation
Electric Power Demands
thermal-mechanical design at both the component and system
levels, andselection and/or pre-treatment of the coolant fluid.
Together these technologiesdefine the conventional thermal
management capabilities and limitations intoday’s gas turbines.
This traditional view of thermal management continues to face
manytechnology challenges today due to the need for higher
efficiencies with lowerspecific fuel consumption. One manner
air-framers are improving fuel efficiencyis replacing traditional
systems with those that operate using electrical power. Forexample,
power from engine compressor bleed air is traditionally used
formultiple purposes including conditioned cabin air, pneumatic
actuation, and de-icing. Using bleed air as an energy source has
several negative effects in regard tofuel usage. It removes air
from the engine, thus directly lowering engine efficiency.In
addition, the piping and all the other pneumatic components are
heavy,further increasing aircraft fuel usage. Electric power
extracted from the engineshaft can be used to energize components
that serve the same function as thosepowered by the bleed air. For
instance, the environmental control system (ECS)traditionally
powered by the bleed air can be operated using a high
efficiencyelectric motor. Electrical based components can similarly
be used to replacehydraulic-based components that require hefty
tubing, pumps, and significantamounts of fluid. Finally, the
operation of increasingly powerful digital avionics
By William D. Gerstler, Senior Engineer, Thermal Systems Lab,
Energy & Propulsion Technologies, GE Global Research Centerand
Ronald S. Bunker, Principal Engineer, Thermal Systems Lab, Energy
& Propulsion Technologies, GE Global Research Center
SPECIAL SUPPLEMENT
TRAVEL ASSISTANCE:IGTI is offering financial assistance for
a
limited number of early career engineers
to attend Turbo Expo 2009. Please visit
http://igti.asme.org for more details.
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December 2008 Global Gas Turbine News 3
SPECIAL SUPPLEMENT
requires the availability of additional on-board power. Figure 1
shows variouspotential electric powered aircraft systems. While
fuel efficiency is one drivertowards more electric aircraft, there
are others including decreased cost associatedwith maintenance and
installation.
The projected growth in on-board electric power is significant
for bothcommercial airliners and military aircraft as depicted in
Figure 2. For example,the Boeing 777 introduced in the mid-1990’s
used about 200kW of on-boardelectric power, but the new Boeing 787
Dreamliner® is expected to demandnearly 1MW. This expansion of
electric power demand is accompanied by adoubling of the power
extraction to thrust ratio (rated kVA/Klbs) for the engines.The
increase in on-board electric power demand is projected to be even
higherfor military aviation, driven by avionics, actuator drives
and controls, andweapons systems advances. A key enabler to
achieving the increased on-boardelectric power is thermal
management. The generators, power electronicconverters/inverters,
motors, and many of the digital electronic devices must bedesigned
with very high power density for aviation applications. If the
losses arenot removed the electrical component can be destroyed due
to overheating. Theeffectiveness of the thermal management system
is the limiting factor indetermining the achievable power
density.
In the past, electric power thermal management was often
achieved withoutmuch regard to the propulsion system and without
significant optimization withthe electric power system. In light of
this, perhaps the single most challengingaspect of the explosive
growth in on-board electric power is the need forintegration of
propulsion, power, and thermal management. The greatlydistributed
nature of the systems requiring electric power, coupled with
their
increasing power densities and operationaltemperature
limitations, leads to the inevitable needfor localized and diverse
thermal solutions. Heatgenerated must either be dissipated/rejected
to thesurroundings, transported for use elsewhere in
theairframe/engine, converted to other energy modes,or stored in
on-board media for later use ordisposal. Other aircraft trends such
as the use ofcomposite fiber materials, decreased volumes of
on-board fuel and oil, and the desire to minimize theuse of any
technology that disturbs the aerodynamicefficiency of the aircraft
and engine (i.e. air-to-liquidand air-to-air heat exchangers)
increase the difficultyin finding adequate thermal management
solutions.Technologies that will play important roles in thesenew
challenges include advanced materials for heatshielding and high
temperature power electronics,heat pipes and their related
technologies, advancedheat sinks including those directly
integrated withelectronic modules and/or those that employ
micro-channel cooling, synthetic jet and spray/mist jetcooling,
nano-fluids, and phase change modules.Effective integration of
these thermal managementtechnologies into the overall system design
will becrucial to successful future aircraft. ✲
Delegates at the 2008 edition of the ASME GasTurbine Users
Symposium found themselves ina new venue. For the first time, GTUS
co-locatedwith Texas A&M’s Turbomachinery Symposium,September
8-11 at the George R. Brown ConventionCenter in Houston.
The new co-location was deemed a success byGTUS Chair, Patrick
Campbell of GE Oil & Gas. “Wesaw resurgence in attendance,”
Campbell said,“demonstrating this is an appropriate
symbioticrelationship, bringing the driven equipment and gasturbine
drivers under one roof.”
Gas turbine users could attend sessions underfour tracks:
Design, Operation & Maintenance,Advances, and Environmental
Issues. Attendeefeedback indicates that Introduction to Gas
Turbineswas among the sessions that were quite popular.
This was a new tutorial, delivered in three parts andprovided a
comprehensive overview into thefunction, performance
characteristics, and typicaloperational issues for industrial gas
turbines. Casestudies as well as discussion were also
incorporatedby the four-man team of expert instructors.
Another highlight of the week was the annualnetworking dinner,
generously sponsored by GE Oiland Gas. In conjunction with GTUS,
IGTI alsopresented two full-day, well-attended workshops,Combustion
Dynamics in Gas Turbine Power Plants andBasic Gas Turbine
Metallurgy and Component Repair.
David Mucz, Manager, Business Operations withAlliance Pipeline,
Ltd., in Calgary, Alberta, Canada,was introduced as the new GTUS
Chair during theplanning meeting at the conclusion of the
event.Mucz will serve a two-year term as Chair. ✲
GTUS08 Holds Successful Co-locationwith Turbomachinery
Symposium
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4 Global Gas Turbine News December 2008
Brayton cycle combustion systems have remainednearly unchanged
in their basic swirl-stabilizeddesign for nearly 50 years. In
recent times, novelconcepts are emerging that have the potential
toimprove combustion system performance. Oneconcept called the
trapped vortex combustor (TVC)was conceived in the early 1990's as
a possiblecombustor design that can provide improvedoperability and
emissions performance. The AirForce Research Laboratory (AFRL) is
investigatingnovel combustion concepts that include TVC, andmore
aggressive high-g ultra-compact combustors(UCC). Both the TVC and
high-g concepts haveshown promise in providing a
reduced-volume,highly efficient and stable combustor. These
shortcombustors enable the use of a UCC in a revolu-tionary
propulsion system that operates on a highlyefficient near constant
temperature (NCT) cycle, orreheat cycle. Such a propulsion system
called theinter-turbine burner (ITB), could enable powerextraction,
thrust augmentation, reduced fuel burn,and specific thrust (ST)
improvements.
Trapped Vortex Combustion: As opposed toconventional
swirl-stabilized combustion systemswhere the flow is stabilized
aerodynamically (seeFig. 1a) a TVC employs cavities to stabilize
the flame
Compact Gas Turbine Combustion Research
(Fig. 1b). A TVC mechanically anchors a pilot recirculation zone
by holding itwithin a specially designed cavity over a wide range
of flow conditions. Primaryfuel and air are injected directly into
the cavities such that the vortex is reinforced.Experiments
indicated that the TVC can reduce pollutant emissions by as much
as60% and improve operability even though the combustor volume is
reduced byalmost 70% for both large-size and small-size engines.
Building on the lessonslearned from TVC, a more aggressive concept
using high gravity (g) combustion,called a UCC, is explored that
can provide even greater engine weight and volumereductions and
become an enabling technology for reheat cycle engines (Zelina,
J.,Shouse, D. T., Stutrud, J. S., Sturgess, G. J., and Roquemore,
W. M., “Exploration ofCompact Combustors for Reheat Cycle Aero
Applications,” AMSE IGTI GT2006-90179).
High Gravity (g) Combustion: In the high-g UCC concept, a cavity
runsaround the outer circumference of the turbine inlet guide vanes
(TIGV), as seenin Fig. 2. The fuel is introduced into this cavity.
Aligned with this cavity, on eachvane, is a radial cavity that
extends to the inner platform. The flow within thiscavity will be
swirled to generate high “g” loading (~1000 g’s) and improvemixing.
The idea is to burn rich in the circumferential cavity, allowing
much ofthe required combustion residence time to take place in the
circumferentialdirection of the engine, rather than the axial as is
done conventionally. Theintermediate products of combustion are
transported into the radial cavities inthe vane surfaces where
combustion continues at a reduced equivalence ratio asthe
mainstream air is entrained into the wakes. Finally, across the
leading edge ofthe vanes, again in a circumferential orientation,
there may be a minimumblockage flame-holder (if necessary) where
products will be entrained anddistributed into the main flow.
Additional air, fed from the interior of the vanes,is introduced
into the radial cavities for cooling and combustion.
By Dr. Joseph Zelina, Air Force Research Laboratory, Propulsion
Directorate
(a) (b)Figure 1: Schematics of: (a) Conventional
Swirl-Stabilized Combustor and (b) Trapped Vortex Combustor.
SPECIAL SUPPLEMENT
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December 2008 Global Gas Turbine News 5
Other system benefits include reduced enginecross-section while
maintaining thrust or poweroutput. Fuel can be axially staged by
independentcontrol of main combustor and ITB to meet
powerrequirements and potentially reduce pollutantemissions. Both
combustion chambers can beoperated at substantially lower
fuel-to-air ratios than asingle chamber, which enables the use of
conventionalmetallic components and increased turbine life by
asmuch as three orders of magnitude! For ground-based,marine, and
turboshaft engines, the combustionsystem can be tailored to meet
low CO and UHCemissions and reduced fuel burn by operating onlythe
main combustor at low-power conditions.
AFRL is in detailed design phase of a UCCcombustor rig that
utilizes a single-sided TVC wherethe TIGV is integrated into the
main flowpath belowthe TVC. The rig will have optical access to
visualizethe flow out of the TVC to the vanes. The rig will
bedesigned with versatility to allow for different vanedesigns,
cavity configurations, materials, and vanecooling schemes. Based on
successful tests of bothTVC and integrated vane designs, this test
willdetermine concept feasibility in a realistic engineenvironment
where operating conditions will be ashigh as 1100 F and 200 psia
inlet temperature andpressure respectively. ✲
(a) (b)Figure 2: Ultra-Compact Combustor Concept.
(a) Schematic Showing Integral Circumferential Cavity and
Turbine Vanesand (b) Ultra-Compact Combustor in Operation.
Functionally, the circumferential cavity may be regarded as a
primary zone, theradial cavities as constituting an intermediate
zone, and the circumferential strutflame-holder as the dilution
zone. All combustion is intended to be completedprior to any flow
turning and acceleration caused by the turbine inlet guide
vanes.Swirl from the compressor may be used to drive the swirl in
the circumferentialcavity. Using the compressor swirl will negate
the need for a stator ahead of thecombustor, further shortening
overall system length.
Future aircraft systems will inevitably require more power
extraction capabilityto support weapons systems, sensor suites,
avionics, and controls. Now thatsubstantial engine length reduction
is realized with the UCC concept, this type ofcombustion system
enables the use of an ITB between the high pressure turbine(HPT)
and low pressure turbine (LPT) spools of the engine. The gas
turbine nowoperates as a reheat cycle which can provide large
amounts of LPT powerextraction with only a 200 ºF – 500 ºF
temperature rise across the ITB.
SPECIAL SUPPLEMENT
Opportunity Fuels and CombustionBy Colin Etheridge, Senior
Consulting Engineer, Solar Turbines Incorporatedand Rainer Kurz,
Manager, Systems Analysis, Solar Turbines Incorporated
Industrial gas turbines allow operation with a widevariety of
gaseous and liquid fuels, while main-taining very low emissions.
Gaseous fuels are notlimited to traditional, pipeline quality
natural gas, butmay include opportunity fuels such as gas available
atoil and gas fields, or products of industrial processes.Today,
many applications require lean premix systemsto achieve the low
emissions necessary.
Lean premix combustors require to thoroughlymix fuel gas and air
at the required mixture ratio priorto the actual combustion. This
allows gas turbines toproduce the very low levels of NOx, CO and
un-burned hydrocarbon (UHC) emissions seen today.Because a
flammable mixture exists prior to theactual combustion, additional
attention has to bepaid too such fuel related properties as
autoignitiondelay time, and flame speed. For a given lean
premixcombustion system, ignoring flashback, autoignitioneffects,
and combustion instabilities, emissions willvary as a function of
the fuel because of differences instoichiometry and adiabatic flame
temperature.
In practice, lean premix injector designs will have to be
tailored to meet thevarious characteristics for any hydrogen rich
fuel and take into consideration anumber of factors which
include:
■ Primary zone stoichiometry for: • NOx emissions • CO emissions
• Combustion stability
■ Flame speed■ Autoignition delay time■ Injector pressure drop■
Combustor oscillations
The laminar flame speed, also called flame velocity, or burning
velocity, isdefined as the velocity at which unburned gases move
through the combustionwave in the direction normal to the wave
surface. A key point here is that theflame speed does not vary
linearly between the respective pure values of themixture
constituents. For example, the addition of H2 to CH4 does not have
asignificant impact upon the flame speed until H2 is the dominant
constituent ofthe mixture. Adding diluents, like CO2, lead to a
flame speed lower than for thenon-diluted mixtures, even if the
temperature is maintained by increasing theequivalence ratio. Flame
propagation velocity is also strongly influenced by thefuel/air
mixture ratio; the leaner the mixture the lower the velocity.
...continued on page 6
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6 Global Gas Turbine News December 2008
SPECIAL SUPPLEMENT
Opportunity Fuels and Combustion ... continued from page
5However, most issues are related to the turbulent flame speed,
which depends,
besides the laminar flame speed, also on the turbulence levels
of the gases inquestion. In particular, data show that as the
turbulence intensity increases, theturbulent flame speed initially
increases, then asymptotes to a constant value, andthen at very
high turbulence intensities begins to decrease. For a given
turbulenceintensity and a given burner, fuels with higher laminar
flame speeds should havehigher turbulent flame speeds. However,
turbulence intensity and laminar flamespeed alone do not capture
many important characteristics of the turbulent flamespeed. Two
different fuel mixtures having the same laminar flame
speed,turbulence intensity and burner can have appreciably
different turbulent flamespeeds depending on the diffusion
characteristics of the species involved.
If the flow velocity in the combustor exceeds the flame
propagation velocity,then flameout could occur. If the flame
propagation velocity exceeds the flowvelocity, then flashback
within the premixing injectors could occur that cancause damage by
overheating the injector tips and walls. To maintain flamestability
at a point, the velocity of the fuel-air mixture must be within the
flame-propagation speed to prevent flashback .
Autoignition is a process where a combustible mixture
spontaneously reactsand releases heat in absence of any
concentrated source of ignition such as aspark or a flame. Rather
than the flame propagating upstream into the premixingsection,
autoignition could cause the spontaneous ignition of the mixture in
thepremixing section. Leaner mixtures tend to have a longer delay
time, whilehigher mixture temperatures and higher pressures tend to
shorten the delay time.In a lean premix injector, the flow
velocities thus have to be high enough toavoid autoignition inside
the injector at the prevailing temperatures. Increasingthe content
of heavier hydrocarbons in an associated gas leads to a decrease
ofdelay time. This is mainly caused by the non-symmetry of all
higher hydro-carbons: Heavy hydrocarbons can be attacked much
easier than methanemolecules, resulting in reduced ignition delay
times.
In general, the characteristic kinetic times decrease with the
addition of hydrogen,with the lowest times (and hence faster
chemical kinetics) corresponding to mixturesof CO and H2. The
longest times (and hence slower chemical kinetics) are attributedto
the mixtures containing mostly methane. In general, few data are
available forspecific mixtures, and engine specific tests are often
necessary to avoid problems.
Another important parameter is the ratio of flammability limits.
In the combustor,the fuel and air must be continually burned to
keep the engine running. When theflame in the combustor is
extinguished it is called a flameout or blowout. The fuelto air
ratio changes with the engine load, as described earlier. In order
to preventflameout the combustor must support combustion over a
range of fuel to air ratios.Each fuel composition has its own
flammability range (Ratio of FlammabilityLimits). If the engine
required fuel to air ratio range is equal to or larger than thefuel
flammability range, then at some point the engine will experience
flameoutand will not be able to operate at that point. Knowing the
ratio of flammabilitylimits allows a decision whether the fuel
composition has a broad enoughflammability range to support
combustion for all operating points of the engine.
The ratio of flammability limits is defined as the upper
flammability limit dividedby the lower flammability limit. The
upper flammability limit is the maximum fuelpercentage (volumetric)
mixed with air that will still light and burn when exposedto a
spark or other ignition source. The lower is the minimum fuel
percentage tosustain combustion. Different gases have different
ranges of flammability.Hydrogen, for example, will burn with as
little as 4 percent fuel and 96 percent air(lower limit) and as
much as 75 percent fuel and 25 percent air (upper limit) atambient
pressure and temperature. Outside of this range (less than 4
percent ormore than 75 percent fuel) the hydrogen-air mixture will
not burn. Thereforehydrogen has a ratio of flammability limits of
75/4 equal to 18. On the other hand atypical coal gas has a ratio
of 13.5/5.3 equal to 2.5. Coal gas typically containsmethane, CO2,
and CO. CO2 is not combustible. Therefore, if the coal gas
containstoo much CO2 the flammability range will decrease and this
ratio of flammabilitylimits will decrease as well.
The different reaction kinetics of different fuelgases impact
combustion dynamics. Different fuelproperties of gases with higher
amounts of heavierhydrocarbons, carbon monoxide, or hydrogen have
tobe evaluated regarding the impact on the resistance ofthe
combustor to oscillations.
Fuel issues are not limited to combustion itself.Potential
hazards associated with fuel, includingflammability, detonation
limits, and autoignitiontemperatures must be considered inside and
aroundthe engine in case of unintentional fuel leakage.Turbine
enclosures are usually equipped with gasdetectors, and the
enclosure ventilation system isoptimized to avoid accumulation of
leaked gases.Low molecular weight gases, which rise rapidly, maybe
trapped in high dead spots in the enclosure,while heavy gases tend
to accumulate on the groundor in low spots. In case of leakage,
accumulationabove the flammability limits must be avoided.
Fornon-luminous gas fires (especially hydrogen), firedetection may
be difficult. Negative Joule Thompsoncoefficients will cause the
fuel gas temperature torise during isenthalpic expansion (for
examplethrough a leak), which may result in an explosion
ifautoignition temperatures are reached. This is aspecial concern
with hydrogen rich fuels. Toxicgases, especially the odorless ones,
require specialsafeguards against leakage.
The quality and composition of fuel burned in agas turbine
impacts the life of the turbine, particularlyits combustion system
and turbine section. Theimpact of physical and chemical
characteristics of gasfuels for gas turbines were linked with
combustioncharacteristics, and the resulting concerns. ✲
References:
Lefebvre, A.H., 1998, Gas Turbine Combustion, 2nd Ed.,Taylor and
Francis, Philadelphia
Lieuwen, T., McDonell, V. ,Petersen, E., Santavicca, D.,2006,
“Fuel Flexibility Influences on Premixed CombustorBlowout,
Flashback, Autoignition , and Stability”, ASMEpaper
GT2006-90770.
Santon, R.C., Kindger, J.W., Lea, C.J., 2002,
“Safetydevelopments in gas turbine power applications”, ASMEPaper
GT-2002-30469
ABOUT IGTIIGTI is an institute of ASME. For
more info on IGTI's conferences
and other membership benefits,
visit http://igti.asme.org.
-
IGTI and the Professional Development Committee are hosting two
courses and two workshopspreceding the opening of “Turbo Expo 2009”
in Orlando, Florida. Don’t miss the uniqueopportunity to
participate in these highly focused training programs in four
specific topic areas. To register or for more information, visit
http://asmeconferences.org/TE09/ShortCourses.cfm
Saturday, June 6, 2009:Workshop I: Basic Gas Turbine Metallurgy
and Repair Technology WorkshopInstructed by Lloyd Cooke and Doug
Nagy, Liburdi Turbine Services
This workshop will explain super-alloy materials, component
damageexperienced from service exposure, techniques used to analyze
the remaininglife of components removed from service, protective
coatings, componentrepair technologies, and quality assurance of
repairs. The workshop includesmany case study examples and the last
section is devoted to a workshop whereattendees develop component
repair solutions. Participants may submitquestions in advance
regarding repair issues faced in their jobs.
HIGHLIGHTS• The workshop provides answers to common questions
and issues for engine
support staff• What makes super-alloys especially suited for gas
turbine components• How do the different damage mechanisms affect
the component - oxidation,
corrosion,. erosion• How are high cycle fatigue, low cycle
fatigue damage caused, prevented, and
repaired• What are the various heat treatments used in repairs,
and why are they important• What are the advantages, disadvantages
of the many types of protective coatings• What are the critical
quality control steps in component repair• How can you reliably
extend the service life of these valuable components
Saturday & Sunday, June 6-7, 2009:Workshop II: Physics-Based
Internal AirSystem ModelingInstructed by Dr. Bijay K. Sultanian,
Siemens Energy, Inc.
The overall purpose of this course is to develop aclear
understanding of the underlying flow and heattransfer physics and
the corresponding mathematicalmodeling and robust solution
techniques for variouscomponents of an internal air flow system
designedfor cooling and sealing of critical parts of modern
gasturbine engines.
After completing this course, participants shouldbe able to:1.
recognize flow and heat transfer physics of various
components of gas turbine internal air systems 2. design more
accurate and solution-robust internal
air flow network models 3. detect input and modeling errors in
their flow
network models 4. interpret results from their models for
design
applications 5. significantly improve their engineering
produc-
tivity and company’s design cycle time
Saturday & Sunday, June 6-7, 2009:Workshop III: Gas Turbine
Aerothermodynamics & Performance ModelingInstructed by Syed
Khalid, Rolls-Royce North America
This workshop will provide review and reinforcement of relevant
thermo-dynamic and aerodynamic concepts as applied to gas turbine
engines, andperformance calculation methods.
Participants will work out typical problems in the class during
recitationsessions facilitated by the instructor. The course
material has been evaluated bythe Department of Mechanical and
Aerospace Engineering of North CarolinaState University.
After completing the course the participants will be able to:1.
apply aerothermodynamic concepts to the analysis of gas turbine
engines 2. analyze turbomachinery velocity diagrams and relate
those to thermo-
dynamic parameters. Learn about the degree of reaction and the
radialequilibrium equation.
3. become familiar with the discipline of operability and
combustorcharacteristics.
4. analyze cycle analysis problems in class on integrating the
componentperformances to get the overall engine performance.
Problems include bothaircraft engine and shaft power cycles.
5. comprehend:i) the method of sizing the critical flow path
areas at the design pointii) the method of satisfying conservation
laws to achieve cycle balance at
off-designiii) the technique of the multivariable solver used in
cycle modelsiv) the various engine cycles in the power generation
field
PROFESSIONAL DEVELOPMENT
December 2008 Global Gas Turbine News 7
SPECIAL SUPPLEMENT
Sunday, June 7, 2009Workshop IV: Film Cooling &Technology
for Gas Turbines Co-sponsored by VKI (Von Karman Institute) and
IGTI
IGTI is proud to be partnering with the von KarmanInstitute to
offer a one day workshop modeled fromone of their week long lecture
series on Film Cooling.VKI is a non-profit international
educational andscientific organization, hosting three
departments(aeronautics and aerospace, environmental and
appliedfluid dynamics, and turbomachinery & propulsion).
Itencourages ”training in research through research”.
INSTRUCTORS AND TOPICS:• Ron Bunker, GE Global Research, will
address
turbine film cooling design, uses, issues,
realities,conservatisms, limitations, and manufacturing
• Tony Arts, VKI, will address the fundamentalphysics and basic
flow field interaction
• David Bogard, will address the main parametereffects on
adiabatic effectiveness and heat transfer /net heat flux; and new
geometries
• Sumanta Acharya, will address computational filmcooling
methods using RANS, URANS, LES, andDNS ✲